The surface area of filter media is a major factor in determining flow resistance (i.e., pressure drop) and loading capacity of a pleated filter. The surface area of a pleated filter media is determined by the size of the pleated filter, the depth of the pleats, and the pleat density. Since the external dimensions of pleated filters are often restricted by the particular application, the number of pleats per inch (pleats density) can be increased to improve filtration performance.
The ability of air filter media to withstand operating pressures is typically dependent upon the pleat count, the pleat depth and the stiffness of the filter media. The filter media can become unsteady when air pressure is applied to one side. In the event the pleats deform or collapse, a portion of the surface area can be reduced and the pressure drop across the filter element will increase, further increasing the force applied to the filter media.
U.S. Pat. No. 5,618,324 (Sommer et al.) discloses a self supporting, accordion folded filter element that includes a planar reinforcing strips bonded to the pleat tips by an adhesive.
A filter element available from Columbus Industries available under the product designation Microshield utilizes a glue bead to provide longitudinal stabilization. The glue bead is applied before the folding of the filter media and connects the folds with one another at the point of application. However, the glue beads require a large quantity of melt bonding agent, resulting in increased cost. Additionally, the glue beads require the pleats to be closely spaced limiting application of this technique to pleat counts generally greater than about six pleats per inch.
U.S. Pat. No. 4,547,950 (Thompson) discloses a method of spacing the folds of a pleated filter media using a tapered assembly comb having uniformly spaced teeth. Subsequently, a rigid divider is inserted into the separated and folded media to produce a uniformly spaced filter media. Thompson does not disclose automated filter element manufacturing.
Therefore, there is a need for an automated method of manufacturing a pleated filter that has good flow characteristics and exhibits sufficient stability so that the pleats do not collapse or deform when subjected to operating pressure.